TOPIC:

Yes, it might be a broken plastic drive gear. But, it could be simpler. A common failure is the horizontal machined slot in the end of the aluminum impeller shaft "rounding out" allowing the impeller to spin on the shaft. If only the impeller spins and the shaft is stationary, the impeller is bad. If both impeller and shaft spin, then the plastic gear is probably bad.

The shaft has a flat place machined on it to accept an open end wrench during assembly/disassembly. The wrench keeps the shaft stationary and prevents breaking the plastic gear while loosening/tightening the bolt on the end of the shaft.

Incidentally, I think there is a mistake in the factory manual regarding this. The manual says do not use the wrench on the shaft while tightening the bolt. It is my opinion that the wrench must be used to hold the shaft stationary when loosening or tightening the bolt to prevent breaking the plastic gear.

globemaster wrote:
The manual says do not use the wrench on the shaft while tightening the bolt. It is my opinion that the wrench must be used to hold the shaft stationary when loosening or tightening the bolt to prevent breaking the plastic gear.

your opinion is correct, the manual also states " USE a 12 mm open end wrench on the water pump drive shaft to keep the shaft from turning" diagram E101 page 74

But it also gives a caution not to use it. its probably meant to say dont use the wrench on one shaft while working on the other

i think as long as you use a 12 mm wrench on the relevant shaft that you are working on to protect the nylon gears is best practise.
and just to add i would use two 12 mm wrenches side by side to give plenty of support. when i rebuilt my engine the previous owner had rounded of the wrench location on the shaft giving me loads of grief trying to remove the sprocket bolt and then find another shaft..

Ian

Thanks for all the replies, going to have a look now. Let you know what I find.

Well, the head has definitely gotta come off so it's just turned into a winter project. I used a battery bearing puller modified to pull the impeller off. Found it is the plastic gearing, so the head comes off soon.
Thanks again for all the replies, let you know how it goes.